The goal of Dr. Fernald's research program is to discover how social interactions are translated into functional changes in the brain. Specifically, I propose experiments that will examine the role of cortisol in cellular change following the recognition of social opportunity among male teleosts. Previous research has shown that the cortisol-mediated "stress" pathway is in part responsible for transduction of social information into cell-specific action. Cortisol levels directly reflect the changes in social status as well as the general stability of the community. Non-territorial males have higher cortisol levels than territorial males in stable social situations. The question remains whether cortisol is simply a correlate of social status or if it predisposes a particular social state. Preliminary evidence obtained in the Fernald laboratory indicates that increasing cortisol levels in dominant males decreases their aggressive behavior, reduces the production of gonadotropin releasing hormone (GnRH) from neurons in the POA, and produces a switch in behavioral phenotype from territorial to non-territorial male. However, prior studies only elevated cortisol levels for a relatively short time. Since this initial attempt, new procedures and techniques have been developed to overcome this limitation. Thus, we are now able to propose experiments to test directly the effects of either increasing or decreasing circulating cortisol on individual and social behavior. The experiments planned will allow us to understand exactly where and how cortisol fits into the causal control pathway through which social behavior changes the brain.